Rock and Mineral Feedstock Characterization

This Module provides the requirements and recommendations for the characterization of solid rock and mineral feedstocks that may be used in carbon dioxide removal (CDR) projects by Project Proponents. This Module is intended for use in conjunction with other Isometric Protocols and Modules. This Module can be used in any instance where physical and geochemical characterization for the use of a rock or mineral material as a feedstock is required by a Project Proponent.

The characterization requirements and recommendations outlined within this Module are based on best known scientific practices at the time of writing. Requirements may be updated in future versions of this Module in line with changes in scientific consensus. This Module outlines methodologies that may be employed to characterize feedstocks to the best of the Project Proponent’s ability, considering scientific rigor, method employment economics, best practice and feasibility. Specific analytical method standard details are outlined in Appendix 1.

Within this Module framework, the key physical and geochemical characteristics of rock feedstocks required for CDR pathways are outlined. Requirements that are specific to different feedstock types, such as commercially produced feedstocks and waste products, are clearly differentiated in distinct sections of this Module. It is a requirement that all feedstocks are characterized, prior to application, to ensure safety and suitability for CO₂ removal. We outline the core feedstock characterization requirements and recommendations in Table 1. The requirements and recommendations outlined here apply to all pathway level Protocols that utilize this Module unless otherwise specified in the Protocol. Any deviations from these requirements outlined in a Protocol will supersede the requirements listed below. These characterization parameters are outlined in more detail in Section 3.

Table 1: Feedstock Characterization Requirements and Recommendations

The characterization requirements outlined in Table 1 are a summary of requirements for feedstock used within a Crediting Project. Where a feedstock is sourced from an extractive process, such as surface or sub surface mining, or has been designated a waste product, further characterization may be required based on relevant regulatory requirements. A summary of such characterization methods specific to mining related feedstock is given in Section 3.5.5.

In some instances, determination methods other than those listed as required in Table 1 may be appropriate. Project Proponents may, in consultation with Isometric, conduct alternative analyses with adequate justification in the Project Design Document (PDD).

It is a requirement of all Project Proponents utilizing a rock or mineral feedstock that documentation is submitted to the Project's Validation & Verification Body (VVB) that outlines the origin and nature of the utilized feedstock. This documentation should form a distinct Section of the PDD and should contain the following information:

• A general description of the feedstock.
• The location the feedstock was recovered/collected from.
  
  This must include:
  • The name of the recover location (such as the mine or quarry name)
  • Location coordinates
  • If the feedstock has been recovered from a ‘waste’ facility, this should be indicated
  • Geological maps and deposit descriptions
  
  
• How the feedstock was recovered from the location
  
  This must include:
  • Sampling and recovery processes from the feedstock source location
  • A description of how the material was transported to the Project location from feedstock source location (see Section 5.3 for Chain of Custody guidelines)
  
  
• A description of any pre-processing that has occurred on location or prior to the feedstock characterization program
  
  This must include:
  • Any pre-processing that has been undertaken on the feedstock after its collection from its source location (such as a tailings storage facility), but prior to geochemical or physical characterization
  • Such processing may include, but not be limited to, crushing, milling, drying and the creation of a representative composite sample

Note: Where a feedstock has been produced by a commercial feedstock producer, the Project Proponent may submit a summary of pre-processing and production procedures. Such summaries should be signed off by the commercial feedstock producer for accuracy.

• An outline of any prior geochemical or physical characterization carried out on the feedstock by the organization that produced the feedstock
  
  This may apply when:
  • Feedstocks are recovered from a waste facility, such as a tailings storage facility (TSF), where characterization is carried out by the feedstock producer
  • Feedstocks are procured from a commercial feedstock producer and are commercially available — feedstock producers may carry out their own characterization program

Note: While prior geochemical and physical characterization data may be submitted to meet the requirements of this Module, the suitability of such submissions will be assessed on a Project by Project basis. Where prior characterization is deemed not suitable for submission, the Project Proponent is required to carry out supplementary characterization of feedstocks, see Section 5.2.

If any of the information listed is not available at the time of PDD submission, Project Proponents must provide adequate supporting documentation to explain why. Such circumstances may occur in relation to the use of mining waste materials, where some information may be made confidential by the entity that produced or provided the feedstock to the Project Proponent.

If the rock or mineral feedstock has been recovered as a by-product of an extractive process, such as mining or quarrying, the Project Proponent is required to report on the legal status of the source material before use in a Crediting Project. This requirement will apply where a feedstock may have been previously, or is currently, defined as a waste product under relevant national regulations and laws. Project Proponents are required to outline and report how such ‘waste’ products have been handled and repurposed as a CDR feedstock, providing specific evidence that its use within a Crediting Project does not breach any local or national laws and regulations. Such national regulations include the Extractive Waste Directive 2006/21/EC within the European Union.

There are a wide range of characteristics that can influence a feedstock’s weathering or dissolution rate for CO₂ removal. These include both physical properties (e.g., particle size distribution, permeability, etc.) and geochemical properties (e.g., mineralogy and elemental composition). Understanding how these characteristics interact with environmental variables to determine these rates is still an active area of scientific investigation. This Module is designed not just for material characterization, but for furthering scientific understanding of feedstock reaction rates.

All projects are required to demonstrate that solid materials utilized as feedstock in CDR projects have been characterized in line with the relevant national standards of the country that the Project is located within. If there is a lack of distinct relevant standards to meet the minimum requirements of this Module, Project Proponents are required to utilize methods outlined by the International Organization for Standardization (ISO). All projects are required to clearly report the standards that are utilized to characterize feedstock materials, with any amendments to standard operating procedures (SOP) or deviations from the relevant ISO or national standard outlined within the PDD upon submission to the relevant VVB, see Appendix 1.

Where specific standards do not exist for analytical techniques, the Project Proponent is required to provide an SOP for the analysis undertaken that can be reviewed by Isometric and the VVB. Such situations may occur for specific analysis, such as XRD based mineralogical analysis, where methods and SOPs may be defined by the instrument manufacturer. In such cases these SOPs must be clearly defined, with reference to specific manufacturer documentation.

Similarly, there may be instances in which the most accessible analytical testing facilities do not conform to ISO or other standards, and instead utilize their own in-house methodologies. Such deviations may be permissible and require explicit approval by Isometric.

Note: Where analysis is carried out by a third party organisation, such as a commercial feedstock producer or external laboratory facility, it is the responsibility of the Project Proponent to retrieve information on standards, methods and SOPs utilized in the characterization of Project Feedstocks, see Section 5.2 for further guidance.

All sample preparation, identification, sub-sampling and storage must be undertaken in accordance with International or national standards. Project Proponents must clearly outline the standards, methods and SOP’s utilized in the preparation and sampling of rock and mineral feedstocks within the PDD.

It is recommended that Project Proponents undertake preparation of samples for geochemical analysis in line with one of, or a combination of, the following standards:

• ISO 23909:2008 - Soil quality — Preparation of laboratory samples from large samples
• BS EN 14899:2005 - Characterization of waste. Sampling of waste materials. Framework for the preparation and application of a sampling plan
• CEN/TR 16365:2012 - Characterization of waste - Sampling of waste from extractive industries
• EN 15002: Characterization of waste – Preparation of test portions from the laboratory sample

When extractive ‘waste’ materials, such as mine tailings, are utilized as a Project feedstock, Project Proponent must follow industry specific standards and SOP’s, such as those outlined in the CEN/TR 16365:2012 standard. Any deviations from methods within a utilised standard must clearly be outlined and justified within the PDD.

Note: A Project Proponent is responsible for ensuring standards are followed by third parties, such as partner laboratory facilities.

Sample preparation and pre-processing procedures must be designed to ensure feedstock samples submitted for characterization are representative of feedstocks used in the Crediting Project. For example, feedstock samples submitted for mineralogical analysis, via XRD or SEM-EDX, should neither be sonicated or washed during sample preparation, to avoid the potential removal of clay mineral phases.

Project Proponents must give each sample a unique ID or sample code that can be used to track samples throughout the feedstock characterization program. This sample ID / code must be consistently documented throughout different analysis types, as well as during the storage of samples.

Project Proponents must outline and describe how feedstock samples were handled and stored, both before and following the planned characterization program. It is recommended that Project Proponents follow the guidelines outlined within ISO 18400-102:2017 (or equivalent). The following should be considered when handling and storing feedstock samples:

• The storage environment must not affect the targeted parameters of the characterization program
• Sample containers should be composed of materials that do not impact the material characteristics (geochemical and geotechnical). Suitable materials include High-density polyethylene (HDPE) or glass
• Sample container headspace should be minimized to restrict potential oxidation and carbonation reactions
• Where samples are stored for an extended period prior to characterization , storage conditions should be designed to minimize and restrict the continued weathering of feedstocks

Note: Available sample duplicates should be maintained in storage for minimum of 6 months following Project Validation

Project Proponents must determine the specific number of samples or replicates that need to be collected for any one batch of feedstock. Project Proponents must conduct characterization of every batch and justify the sampling procedure and number of analyses based on project-specific considerations. Project Proponents are responsible for reporting the homogeneity of the feedstock to Isometric, ensuring that data are spatially representative of the entire project area and that sampling captures both horizontal and vertical variability within the feedstock used in a Crediting Project. Projects must demonstrate the degree of homogeneity within a single feedstock batch.

Projects that utilize a commercially available feedstock, where validated characterization data is provided by the feedstock producer, are not required to implement a specific sampling plan in instances where the data provided satisfies the requirements of this Module.

Note: For the purpose of this Module, we define a batch as a unit of feedstock sourced from a particular location at a particular time that is processed and transported as a single unit.

Where data and information provided by commercial feedstock producers does not meet all of the requirements of this Module, additional analysis may be carried out by the Project Proponent. In such instances the Project Proponent is required to outline a sampling plan for additional characterization analysis.

The Project Proponent must consider a broad range of feedstock characteristics and relevant context that may influence rock homogeneity when determining a sampling plan. These considerations include, but are not limited to, grain size distribution, particle sorting that may occur during processing and transport, the amount of feedstock being spread and the geological/geochemical setting from which the feedstock was extracted.

Note: All relevant details of the sampling plan, number of analyses, and adequate justification for these choices must be included in the PDD.

Recommended methods for assessing feedstock homogeneity include compositional variance analysis, such as ANOVA (Analysis of Variance), performed on major element or mineralogical characterization data; field screening techniques using handheld XRF or near-infrared spectroscopy; and approaches such as the ITRC Incremental Sampling Methodology¹, which suggests collecting a large number of small increments — typically 30–100 — systematically and randomly distributed throughout the bulk feedstock pile. It is acknowledged that rock feedstocks are likely to vary in composition as an extractive material, depending on the source location.

Project Proponents must include in the PDD a detailed description of how the chosen sampling plan addresses any heterogeneity that might be present within the batch. This may include sampling across horizontal and vertical dimensions of a feedstock batch as a consideration of particle sorting that may happen during processing and transportation.

To determine the variability of a feedstock material, is it recommended that Project Proponents use relevant ISO standards, such as those outlined in Table 2 below.

For example, Annex 2 of ISO 3082:2017 outlines a variability experiment using duplicate sampling, where

• High Variability (Heterogeneous): More increments are required (e.g., n = 50+ for a 1,000-tonne material mass)
• Low Variability (Homogeneous): Fewer increments are required (e.g., n = 10–20)

Note: The variability of feedstock materials, and subsequent sampling increments (n), must be demonstrated and justified within the PDD. A Project Proponent must outline the specific method used to assess variability, such as compositional variance analysis (such as ANOVA).

Table 2: Example ISO standards that may be utilized when designing a sampling plan

In line with ISO 3082:2017 sampling increments, composite sampling and aliquots are defined as follows:

• Increments: These are the individual sample masses taken across a feedstock stockpile (e.g., 50 individual bulk samples)
• Composite Sample: All collected increments are combined and mixed thoroughly. This "averages out" the variability of the rock, creating a ‘representative’ composite
• Laboratory Sample: The composite is representatively split down to about 1–2 kg sub-samples to send to a laboratory facility for characterization
• Aliquots: The laboratory may reduce sample sizes (e.g., 0.5g) to utilise in individual analysis methods.
• Replicates: 2 or 3 aliquots (Replicates) are typically tested to demonstrate the laboratories analysis accuracy

Project Proponents are required to collect a minimum of 40 representative sample increments from their feedstock source in order to create a composite sample mass for characterization. The sampling plan employed to collect sample increments must be described in detail within the PDD.

Note: All Information related to the creation of composite samples, laboratory samples and aliquots for the purpose of feedstock characterization must be outlined within the PDD upon submission. Information must include utilised material characterization, preparation and sampling standards, methods and SOPs (where applicable).

While Project Proponents are required to collect a minimum of 40 representative sample increments from their feedstock source (e.g. stockpile or TSF), it is highly recommended that Project Proponents follow the methods and guidances outlined in relevant ISO standards.

For example, where a specific standard deviation is not known for a feedstock yet, ISO 3082:2017 (Annex 2) recommends default sample increment numbers based on the mass of the feedstock source / stockpile and the variability of the feedstock (high or low). Table 3 outlines recommended sampling increments, in line with ISO 3082:2017 (Annex 2).

Table 3: Recommended Sample Increments for high and low variability feedstocks

Note: Alternative sampling increment plans may be acceptable where Project Proponents can demonstrate statistical representativeness, or in instances where Project Proponents have followed a specific ISO standard for sampling and sample preparation

Where characterization has been carried out by a commercial feedstock producer, the producer is not required to submit a sampling plan for review. In instances where a further characterization is carried out on commercial feedstocks by the Project Proponent upon receiving the feedstock, a sampling plan should be submitted for the additional characterization program.

The physical properties of rock and mineral feedstocks are required to be characterized before use in a Crediting Project. Physical characteristics are required to be assessed in line with the methods and standards outlined within this Module. Within this Module, physical characterization covers a material's geotechnical and physical characteristics.

It is required that all materials are characterized for their geotechnical properties, unless specifically specified within a Protocol. These properties are key to understanding the physical nature of utilized rock feedstocks at the time of analysis. Key parameters may include water content, specific gravity, particle density, bulk density and permeability.

Project Proponents are required to undertake geotechnical investigation and testing. The exact set of tests required will vary on a project basis, but should generally be in line with the ISO standards group ISO 17892. This standard set is listed below, with feedstock-specific requirements highlighted.

Required for all pathways, unless otherwise specified in a pathway Protocol:

• Determination of water content - e.g., ISO 17892-1:2014
• Determination of particle size distribution - e.g., ISO 17892-4:2016

Recommended for all pathways, unless otherwise specified in a pathway Protocol:

• Determination of bulk density - e.g., ISO 17892-2:2014
• Determination of particle density - e.g., ISO 17892-3:2015
• Incremental loading oedometer test - e.g., ISO 17892-5:2017
• Fall cone test - e.g., ISO 17892-6:2017
• Unconfined compression test - e.g., ISO 17892-7:2017
• Unconsolidated undrained triaxial test - e.g., ISO 17892-8:2018
• Consolidated triaxial compression tests on water saturated soils - e.g., ISO 17892-9:2018
• Direct shear tests - e.g., ISO 17892-10:2018
• Permeability tests - e.g., ISO 17892-11:2019

A Project Proponent is responsible for ensuring that all geotechnical laboratory testing undertaken on rock and mineral feedstock materials meet standards in accordance with national regulations in a project's location. If a Project Proponent or partner facility undertakes testing in line with a national alternative to the aforementioned ISO standards, this must be reported within the Project PDD.

Projects are required to carry out particle size distribution (PSD) and specific surface area analysis for all rock and mineral feedstocks used within Crediting Projects. Within this Module, gravimetric sieving and BET analysis are required to determine these parameters.

Gravimetric Sieving

It is required that all proposed rock and mineral feedstock materials are analyzed for particle size distribution through gravimetric sieving. It is required that all Project Proponents carry out this analysis in line with the ISO 11277:2020 or ISO 17892-4:2016 standardized procedures, or an equivalent national or regional standard. If a Project Proponent chooses to utilize a specific national variation of the ISO standard, such as BS ISO 11277:2020, any variations from the ISO procedures must be clearly reported.

BET Analysis

To quantify the specific surface area of a rock and mineral feedstock materials, it is required that projects undertake BET analysis. This analysis will aid in quantifying the potential reactive surface area of rock feedstock and will aid in estimating the relative reaction kinetics of a feedstock for CDR. It is required that the BET method undertaken is in line with ISO 9277:2022.

Other PSD and surface area techniques

The Project Proponent may, in consultation with Isometric, perform alternate techniques to measure or validate a rock feedstock's PSD or relative surface area. Such techniques, for example, may include small angle X-ray scattering (SAXS) that may be used to estimate mean particle sizes between 1 nm and 100 nm. Where such techniques are utilized by a Project Proponent, the procedures undertaken must be clearly and adequately reported, with reference to SOPs or standards, such as ISO 17867:2020.

Geochemical characterization is required for all proposed rock and mineral feedstock materials. Project Proponents are required to determine the abundance of major and minor elements within a feedstock, the mineralogy of the feedstock, the total elemental carbon and sulfur and feedstock radioactivity using the methods described in the following section.

Elemental characterization is required to establish baseline metal cation and anion contents of a rock feedstock material. Elemental composition evaluation can be carried out using a range of methods, dependent on the exact composition of the feedstock rock. Projects are required to undertake ED-XRF/ WD-XRF or fusion / acid digestion coupled with ICP-MS or ICP-OES on utilized rock feedstocks.

Projects are required to initially characterize rock feedstocks for the following elements at a minimum:

Na, Mg, Al, Si, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Cd, Ba, W, Hg, Tl, Pb and Zr

Initial characterization must also include any elements, isotopes, and/or isotope ratios not listed above that will be used to quantify weathering rates in the field. Following initial assessment of elemental composition, a Project Proponent can refine elemental analysis to reduce the total number of elements measured. Project Proponents are required to demonstrate that eliminated target elements do not represent a measurable portion of the assessed feedstock material. This can be quantified through elemental mass balance calculations.

ED-XRF

Major and minor elemental compositions are required to be analyzed via ED-XRF. This analysis is required as it will allow Project Proponents to identify the proportions of key elements Mg and Ca (often reported as oxides MgO and CaO) within a proposed feedstock material. Major and minor elemental analysis is also required to assess the suitability of a material for use in CDR projects, taking into consideration the concentrations of potentially environmentally harmful elements within a feedstock source.

Note: Data collected by a portable XRF is not eligible for Crediting within this Module. Portable XRF data may be used to demonstrate homogeneity when creating a sampling plan (see Section 3.3.2), but must not be used as a primary elemental characterization analysis method.

Acid Digestion and/or Fusion coupled with ICP-MS/OES

It is required that Project Proponents undertake detailed elemental analysis of rock feedstocks. Although it is acknowledged that digestion, fusion, and fluorescence based analysis methods are not directly comparable, a more detailed level of analysis will potentially reduce analytical uncertainties when characterizing a rock feedstock. At least one of the following analyses are required for elemental characterization:

• Fusion + Two-Acid Digest / Aqua Regia Digest (with ICP-OES/MS)
• Fusion + Multi-Acid (4-Acid) Digest (with ICP-OES/MS)
• Fusion + Nitric Acid Digest Digest (with ICP-OES/MS)

Other elemental measurement techniques

If a Project Proponent chooses to utilize additional elemental measurement techniques, such as Atomic Absorption Spectroscopy (AAS) or WD-XRF, it is a requirement that details of the analyses are outlined within the PDD.

It is strongly recommended that Project Proponents consider the analytical uncertainty associated with various measurement techniques when developing an analytical framework for feedstock characterization. For example, XRF techniques may have sufficient precision to determine major elemental composition, but higher analytical resolution may be required for a full characterization of trace elements. Project Proponents must provide justification for their chosen methods in the PDD, including evidence that there is sufficient analytical resolution to determine the concentrations of trace elements relevant to calculation of weathering rates or to environmental safeguards.

To assess the theoretical maximum carbon removal potential of an alkaline rock or mineral feedstock, Project Proponents must use an adjusted version of the Steinour equation, see Equation 1². The equation uses bulk elemental oxide composition to estimate the maximum CO₂ removal potential of a feedstock material:

$${E_{pot}} = 
(\frac{1000}{100}) \times (\frac{CaO}{M_{W, CaO}} + \frac{MgO}{M_{W, MgO}} + \frac{Na_2O}{M_{W, Na_2O}} + \frac{K_2O}{M_{W, K_2O}} - \frac{SO_4}{M_{W, SO_4}} - \frac{P_2O_5}{M_{W, P_2O_5}}) \times M_{W, CO_2} \times \eta  - C_{feedstock}$$

(Equation 1)

Where:

• $Epot$ is the CO₂ capture potential of an alkaline rock and mineral feedstock used in enhanced weathering, in kg of
  CO₂ per ton of feedstock
• The factor $(\frac{1000}{100})$ is a unit conversion that adjusts oxide weight percentages to kilograms per ton of feedstock
• $Mw$ is the molecular mass of the specific oxide
• All oxides are in the unit of weight percent of the bulk feedstock (i.e., 5 wt% is input as 5)
• $η$ is the molar ratio of CO₂ storage potential to divalent alkalinity released from feedstock. This term has a maximum value of 2
• $C_{feedstock}$ is the carbon content (organic and inorganic) of the feedstock

The adjusted equation utilizes elemental composition to identify maximum CO₂ capture potential of an enhanced mineralization project (Epot) based solely on bulk elemental analysis. The calculation output is in the form of kg of CO₂ per tonne of feedstock and represents the quantitative hypothetical potential of the material to capture CO₂ as bicarbonate or carbonate. It must be noted that this equation does not take into consideration variables that effect carbonation and carbonation rates such as temperature, known reaction rates, pressure, moisture content and PSD. The equation considers the presence of elemental sulfur and phosphorus as having a reducing effect on overall theoretical potential. This is due to two distinct rationales: (1) their dissolution has no implicit reaction with CO₂ directly and (2) they may become acid compounds, producing acidity which has implications on the carbonate system as CO₂ may be produced³.

Elemental abundance data should be produced according to methods prescribed in this Module. The CDR potential calculated in Equation 1 represents the upper limit of Creditable removals for a single batch of feedstock as defined in Section 3.3.1. Project Proponents are required to report the CDR potential of each batch of feedstock used pursuant to project activities in the PDD.

Note: Project Proponents may, in consultation with Isometric, use an alternative version of the Steinour equation, shown in Equation 1, when calculating the theoretical maximum carbon removal potential of a feedstock. The suitability of an alternative approach will be assessed on a Project by Project basis.

It is recommended that the Project Proponent determines the impact of previous chemical alteration and weathering on rock and mineral feedstocks as part of a suitability assessment prior to application. One tool that may be used for aluminosilicate rocks and minerals that are not Mg²⁺ or Fe³⁺ rich, such as plagioclase and other feldspars, is the chemical index of alteration ($CIA$)⁴. This geochemical tool was introduced by Nesbitt and Young (1982) and is commonly used in sedimentary geology, geochemistry, and paleoclimatology to infer the intensity of weathering processes and climatic conditions. The $CIA$ is calculated from the molar proportions of major oxides in a sample, focusing on the loss of mobile cations (like Ca²⁺, Na⁺, and K⁺) relative to immobile aluminum. The $CIA$ has been historically used in the weathering literature^{4, 5, 67, 8, 9} including mafic terrains, and provides the most straightforward interpretation of incipient alteration. The maximum CDR potential of the feedstock will be inherently limited by the initial degree of alteration. Additionally, the $CIA$ value can be used in concert with the mineralogical assessment of the feedstock to evaluate the input of clay minerals from weathered feedstock and/or a source of contamination to the feedstock (e.g., atmospheric dust). The equations uses molar proportions of elements as follows:

$$CIA= \frac{Al_2O_3}{Al_2O_3 + CaO^*+ Na_2O + K_2O} \times 100$$

(Equation 2)

Where $CaO^*$ is traditionally the amount of CaO incorporated into only the silicate fraction, i.e., a correction for any calcium in carbonate or apatite in the feedstock. Pairing the $CIA$ calculation with the mineralogy of the feedstock, this $CaO^*$ correction can be ignored if these phases are absent. Lower values (less than 50) tend to indicate very limited weathering and high CDR potential. Values approaching 100 indicate significant weathering and very low CDR potential. Project Proponents may also consider applying alternative weathering indices that are more appropriate for a given feedstock chemistry (e.g., Mafic Index of Alteration and/or Weathering Intensity Scale).

Analysis of baseline carbon and sulfur contents are required for all rock feedstocks utilized within Crediting Projects. It is recommended that carbon and sulfur analysis is carried out via combustion analysis in line with the following standards:

• Determination of organic and total carbon after dry combustion (elementary analysis) - e.g., ISO 10694:1995
• Determination of total sulfur by dry combustion - e.g., ISO 15178:2000

Total carbon and sulfur content are required as baseline measurements before a rock feedstock can be utilized within a Crediting Project by Project Proponents.

Consideration of feedstock radiation levels is required prior feedstock utilisation by a Project Proponent. At a minimum, the Project Proponent must either determine gross alpha and beta activities or provide adequate, geologically and geographically specific justification demonstrating low radiation levels. The following standard is recommended:

• Measurement of radioactivity in the environment - Soil - e.g., ISO 18589:2019

Where an alternative standard is used, documentation of such standard must be provided to the VVB. The Project Proponent is required to ensure adherence to all applicable local, national and international laws regarding acceptable levels of radiation within the context of the Project.

Note: In some cases, there may be sufficient pre-existing data demonstrating that radioactivity of a certain feedstock, such as commercially available feedstock products, is negligible. Project Proponents may, in consultation with Isometric, choose to submit this pre-existing data with sufficient justification in the PDD.

Mineralogical characterization is required for all rock feedstock materials used within Crediting Projects. Mineralogical characterization can be performed through multiple analytical methods, depending on the feedstock source, target mineral phases and the ability of a Project Proponent to access analytical facilities. Bulk mineral abundance is required for all rock feedstocks, including analysis by XRD and mineral mapping via scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS/EDX).

Mineralogical Analytical Requirements and Recommendations

A combination of XRD, light microscopy and/or SEM-EDS mineral mapping is required to determine a rock feedstock's mineral type and abundance. As XRD can be used for either qualitative analysis, which identifies mineral phases present, or quantitative analysis, which measures the relative abundances of those minerals, quantitative XRD (qXRD) is required when examining mineral type and abundance in feedstock materials. Project Proponents are required to report bulk mineral abundances for all rock and mineral feedstocks used in CDR Crediting Projects.

Project Proponents are required to outline the specific methodology used, with reference to source laboratory SOPs or the utilized equipment’s manufacturer methodologies. Project Proponents choosing to utilize light microscopy for mineralogical characterization are required to send rock samples to an accredited external laboratory for analysis and must cross-check results with qXRD, SEM-EDS and/or geologic information.

Note: Submitted methodology information on the specific mineralogical analysis carried out within a project should include: sample preparation, coating types, instrument calibration and the certified reference materials (CRM) used (where relevant for SEM-EDX/EDS).

Rock Feedstock Mineral Abundance Risk Descriptions and Assessments

When assessing the use of potential rock feedstock within Crediting Projects, Project Proponents must outline key target mineral groups that may pose a project risk. Project risks may include, but are not limited to, the following:

1. Human/health Risk
2. Environmental Risk
3. CO₂ Removal Inefficiency

Mineral groups, including carbonates, sulfides and asbestos group minerals, should be assessed in the context of these risk factors on a project by project basis. A Project Proponent is required to provide detailed quantitative and qualitative descriptions of its feedstock with direct reference to key target mineral groups.

Where a rock feedstock material contains sulfide and asbestos group minerals, a Project Proponent is required to assess the viability of utilizing such feedstocks within a Crediting Project. Such assessments should consider the potential for reversals (for example where the oxidation of sulfide minerals leads to the production of acidity), and environmental harm (e.g., potential for release of fibrous asbestos particles into the environment). A Project Proponent is required to report the findings of these assessments within the PDD upon submission to the VVB and relevant regulatory bodies.

The specific risks related to use of a rock feedstock material will depend on the application of the material within an individual project. Therefore, risk assessments are required on a project by project basis in consultation with the Project registry, VVB and relevant regulatory bodies.

Rock and mineral feedstock sourced from mining operations, both active and closed, may require further geochemical characterization in line with relevant local regulatory requirements. The terms mine wastes/by-products within this Module refers specifically to tailings and waste rock (overburden) materials. Specific geochemical characterization for mining wastes beyond the requirements listed above is not specifically required within this Module, although Project Proponents must demonstrate that any further characterization required by relevant regulatory bodies has been undertaken.

It is recommended that projects that utilize rock feedstocks produced by mining operations undertake a detailed geochemical characterization program. Such programs should include consideration of the potential environmental implication of utilizing such feedstocks within the Crediting Projects. Multiple international guides and standards exist specifically for characterizing extractive wastes such as tailings and waste rock. Project Proponents are responsible for ensuring such wastes are characterized in accordance with local regulatory requirements.

Where specific regulatory guidance on the characterization of mining wastes and by-products does not exist within the locality of a Crediting Project, we recommend that the Project Proponents revert to the mandated characterization standards outlined by the European Commission. These standards provide a detailed baseline for the characterization of rock feedstocks sourced from mining operations. The following standards are recommended:

• EN 15875:2011 Characterization of waste - Static test for determination of acid potential and neutralization potential of sulfidic waste
• CEN/TR 16363:2012 Characterization of waste - Kinetic testing for assessing acid generation potential of sulfidic waste from extractive industries
• CEN/TR 16376:2012 Characterization of waste - Overall guidance document for characterization of waste from extractive industries
• CEN/TS 16229:2011 Characterization of waste - Sampling and analysis of weak acid dissociable cyanide discharged into tailings ponds
• CEN/TR 16365:2012 Characterization of waste - Sampling of waste from extractive industries

Regionally specific mining waste characterization programs may be undertaken dependent on the national regulatory requirements of the Project's host country. Project Proponents are required to report utilized mining waste characterization procedures and methods within the Project's PDD. Project Proponents are required to demonstrate that wastes recovered from extractive processes meet national environmental regulations within the Project's location.

Where a mining operation's waste characterization program follows specific guidance based on best practices, rather than ISO or CEN standards, the Project Proponent is required, and responsible for, outlining the specific methods and procedures that have been utilized to characterize the mining waste materials. Such alternative guides or handbooks may include the following:

• The predictive manual for drainage chemistry from sulfidic geological materials (MEND Report 1.20.1)
• The Global Acid Rock Drainage Guide (GARD Guide)
• EPA 530-R-94-036 (Technical Document - Acid Mine Drainage Prediction)

A Project Proponent is required to report the analytical laboratory/laboratories that have been utilized for feedstock characterization. It is the responsibility of the Project Proponent to ensure that the chosen analytical facilities are reputable and conduct characterization techniques to the required standards indicated within this Module and Appendix 1.

Analysis must be completed by a qualified laboratory, as evidenced by accreditation to ISO 17025 or equivalent standards for laboratory quality management for the specific test method (ASTM D5291).

Laboratories shall complete standard quality assurance procedures on a schedule in accordance with their quality management plans and accreditation requirements to include:

• Analysis of blanks
• Analysis of duplicates
• Instrumentation calibrations and analysis of calibration standards

Project Proponents should utilize UKAS, MCERTS, DWTS and ISO accredited analytical services whenever feasible.

Where a Project Proponent utilizes laboratory facilities within an academic institution, or a non-accredited commercial laboratory, periodic external validation must be undertaken with an accredited facility. At minimum, external validation of all results that directly influence Crediting volumes must be undertaken during a Project's first verification and annually thereafter.

Analysis types that must be externally validated annually include (at a minimum):

• Elemental Composition - ED-XRF, WD-XRF or fusion / acid digestion coupled with ICP-MS or ICP-OES
• Total Carbon and Sulfur - Dry Combustion

Analysis types that should be externally validated annually include:

• Mineralogical characterization - XRD, SEM-EDX

External validation of academic or non-accredited laboratory analysis must be carried out on a minimum of 3 samples, which are either representative or duplicates of samples analysed during the Project feedstock characterization program. Project Proponents are required to report the frequency of external validation checks within their PDD prior to use of a rock material as a feedstock in a CDR Project.

If results of external validation show discrepancy with non-accredited or academic results, Project Proponents must undertake further external analysis to identify the source of discrepancy in order to explain the results. In this case, the choice of results to be submitted for Crediting must be agreed upon with Isometric prior to submission.

Note: Externally validated analysis must demonstrate a <5% discrepancy between the average of the replicates and the non-accredited results submitted by the Project Proponent, where % difference is defined as the calculated % difference (or % error).

Project Proponents are required to report calibration records (where available) from analytical facilities to the relevant VVB when submitting feedstock characterization data. Projects are also required to outline specific analytical checks that have been carried out to maintain data quality, with specific reference to the relevant certified reference materials (CRM) used by the utilized laboratory facility.

Characterization data should be validated through set quality assurance and quality control (QA/QC) criteria within all Crediting Projects. All projects are required to report their QA/QC processes within the PDD, in accordance with the requirements of this Module. As part of QA/QC Project Proponents are required to clearly describe analytical checks (including duplicate, blanks and analytical standards checks) and calibration procedures.

Project Proponents are responsible for providing all feedstock characterization data within the PDD submission. While characterization and analysis must be conducted at an accredited external facility, the Project Proponent remains ultimately accountable for ensuring the data is accurate and externally verifiable. Submitted data reports are required to include results of all utilized standards to verify data quality. Project Proponents are required to maintain data records for a minimum of 5 years following the date of data collection.

Project Proponents are required to report data such that the data analysis methods used are easily identified, verified and replicated. This Module requires that any data reports include the raw data from which any data analysis/reduction was performed, including standards and replicate measurements.

A summary containing information on analytical uncertainty, number of samples taken, standards used and number of standard runs, standard deviation and percentage error on the standards must also be included. This may, for example, take the form of a spreadsheet containing four sheets:

• Summary sheet detailing metadata:
  • Number of samples run
  • Analytical uncertainty
  • Standards used
  • Number of standards run
  • Standard deviation
  • Percentage error on standards
• Reduced data sheet (data summary)
• Data reduction sheet (if applicable; e.g. processing of ICP-MS data)
• Raw data

In instances where characterization data is generated by a third party, such as a commercial feedstock producer or mining operator, such data may be submitted to meet the requirements of this Module. Results and data submissions by third parties must meet all of the requirements of this Module.

Note: Data provided by a commercial feedstock producer does not need to contain raw / meta data files, where results have been externally validated. Raw data sheets and metadata may be requested in instances where further validation of submitted results are required, prior to verification and Crediting.

• Results and data produced by third parties may be submitted by the Project Proponent within the PDD
• Where the third party is unable, or unwilling, to provide results or characterization information (such as utilized methods or internal SOPs) to the Project Proponent, the third party may submit this information directly to Isometric and the Project VVB
• In instances where information will be submitted directly by the third party to Isometric and the VVB, the following must be considered:
  • It is the responsibility of the Project Proponent to identify if Isometric must engage with a third party in order to receive required results or characterization information to fulfill the requirements of this Module
  • Introductions to third parties in such instances should occur as early as possible to reduce potential delays in validation and verification
  • It is the responsibility of the Project Proponent to ensure characterization methods and generated data used to fulfil the requirements of this Module are suitable for submission, even in instances where analysis and data generation is carried out by a third party
  • In instances where results or characterization information submitted by the third party is not deemed suitable by Isometric and the VVB to meet the requirements of this Module, the Project Proponent may be required to undertake this analysis independently of the third party

• Information provided by third parties will be assessed by Isometric and the VVB
• Where agreed, Isometric and the VVB will not share proprietary or sensitive information provided by the third party with the Project Proponent
• Proprietary or sensitive information provided by the third party may be redacted within the public PDD
• Characterization methods must be outlined in all submissions, where an internal SOP is utilised a general summary of the methods and related standards will be accepted (upon review by Isometric)
• Characterization methods and data submission information must include (at a minimum):
  • The analysis type (e.g ICP-OES or ED-XRF)
  • Standard, method or SOP followed
  • QA/QC data and information
• Information may be submitted in an Excel sheet, CSV or PDF (unless submitted directly within a PDD or Isometric Certify)

Note: Any redactions within the public facing PDD on the Isometric Registry must be pre-agreed in consultation with the VVB prior to the completion of Validation and Verification.

Within this Module commercial feedstocks are categorized as feedstocks that are commercially available for purchase by a Project Proponent. Such feedstocks may include Calcium Carbonate that is purposely quarried and produced, and is not a waste or by-product of other extractive activities (such as the mining of rare earth elements).

Where a feedstock has been procured from a commercial feedstock producer by the Project Proponent, the following applies:

• The Project Proponent must provide the information of their commercial feedstock producer to Isometric and the VVB, within the PDD
• Commercial information and characterization data related to the procured feedstock product may be submitted to fulfill the requirements of this Module
• Submitted information on commercial feedstocks must contain all of the required analyses outlined within this Modules previous sections, unless specified otherwise
• If raw data is not available for commercial feedstocks, summarised data for characterization requirements will be considered on a Project by Project basis, in consultation with Isometric and the VVB
• Collection and production information may be summarised for commercial feedstocks, where the information is not easily available to the Project Proponent
• Commercial feedstock submissions do not require external validations, where the commercial feedstock producer can demonstrate adherence with ISO standards for its own internal characterization. Submissions must include a bulleted list of relevant standards and/or SOPs used in the generation of data submitted within the PDD
• Analytical and calibration data does not need to be submitted where the commercial feedstock producer can demonstrate adherence with ISO standards for its own internal characterization
• Distinct radiation analysis is not required for commercially available feedstocks where the feedstock producer can demonstrate negligible radioactivity levels (evidenced by either elemental analysis or geological assessments of the host deposit)
• Sampling plans do not need to be submitted for data generated by a commercial feedstock producer

Note: Where information or results provided by a commercial feedstock producer does not meet the requirements of this Module, it is the responsibility of the Project Proponent to undertake supplementary analysis. In such instances all characterization, sampling and QA/QC requirements will apply. Isometric reserves the right to request full characterization of commercial feedstocks, where information provided by the feedstock producer is not suitable to satisfy this Modules requirements

Project Proponents are required to submit chains of custodies (CoC) that cover feedstock production and transportation, as well as feedstock characterization programs. CoC’s may be categorized as follows:

• Single Chain CoC (Recommended) - A continuous CoC document that covers collection, transport, storage and external characterization of a feedstock sample

• Feedstock Production / Collection CoC - A CoC covering the sourcing of the feedstock by the feedstock producer, through to delivery of the feedstock to the Project Proponent.

• Feedstock characterization CoC - A CoC covering the handling of the feedstocks from the supplier or producer to the characterization location/lab

It is recommended that Project Proponents submit a single chain CoC that covers the production, storage, transport and characterization of a feedstock. Where a single chain CoC is not possible, separate feedstock production and characterization CoCs may be submitted within the PDD.

Chains of Custodies should be created, implemented and utilized in line with either of the following standards:

• ISO 22095:2020 - Chain of custody — General terminology and models
• ASTM D4840-99 Standard Guide for Sampling Chain-of-Custody Procedures

Note: Project Proponents may follow other CoC standards or internal SOP’s, as long as they meet the requirements outlined in this Module section. Where an alternative CoC system or SOP has been implemented the Project Proponent must describe this system within the PDD.

CoCs must be submitted in either table format or directly within Isometric Certify

All CoCs must include the following (at a minimum):

• Document Serial Number
• Project Name
• Project Proponent Name
• Primary Contact
• Batch ID / Number
• Sample ID’s
• Sample Description
• Described actions (transport, storage etc)
• Analysis Requested (for single chain or feedstock characterization CoC’s)
• Locations
• Dates
• Custody Log - including information such as:
  • Relinquished By - Signature, Date, and Time
  • Received By - Signature, Date, and Time
  • Transport Method - Courier name and tracking codes (where applicable)

Appendix 2 contains an example single chain CoC that is recommended for all Projects. The CoC template within Appendix 2 has been designed to be compliant with ISO 22095:2020.

Where commercial feedstocks have been provided to a Project Proponent directly by the feedstock producer, a Bill of Lading (BOL) will be acceptable in place of a Feedstock Production/Collection CoC.

In such instances a Single Chain or Feedstock characterization CoC will still be required for all sampling and analysis carried out by external third party laboratories, including accredited and academic institutions.

Submitted CoCs for commercial feedstocks must contain the following (in place of transport and storage information):

• Information on the feedstock producer (Name)
• The BOL number
• The date the feedstock was shipped
• Who received and signed for the materials (Physical or digital signature)
• How the material was stored by the supplier upon being received

Note: In instances where sampling and characterization programs are carried out entirely by a commercial feedstock producer, prior to direct delivery of the feedstock to the Project Proponent, a BOL may be accepted in place of a full CoC. In such situations a simplified CoC may be required where samples are stored by the Project Proponent, prior to use in Crediting Projects.

If the feedstock used constitutes a waste product that was not mined or quarried specifically for project activities, the counterfactual fate of the feedstock may yield some level of baseline carbon removal.

Project Proponents must:

• Describe the counterfactual fate for the feedstock (the baseline scenario)
• Quantify the counterfactual feedstock weathering which would have occurred in the absence of the Project

Note: The counterfactual fate for feedstocks will vary. Two dominant modes of counterfactual weathering and their respective requirements for quantification are described below. If other forms of counterfactual feedstock weathering are relevant, a quantification strategy must be described in the PDD and approved by Isometric.

If the counterfactual fate of the feedstock is storage in open-air conditions, some degree of surficial weathering could be expected. For projects where the feedstock would have counterfactual surficial weathering:

• Surficial weathering must be calculated using geochemical modeling of feedstock weathering under storage conditions relevant to the source site
• Project Proponents must provide a written description of the storage site
• The model must accurately reflect the feedstock mineralogy, surface area, and CDR potential, based on the data reported for feedstock characterization
• The model must accurately reflect the baseline carbonation, permeability and water saturation of the tailings pile, based on direct measurements of the tailings pile over the course of a Crediting Project. Inclusion of microbial activity in the feedstock pile is recommended
• The model must accurately reflect the environmental conditions of the source site, including temperature, average annual precipitation, rainwater pH and carbonate saturation, groundwater pH and carbonate saturation, based on direct measurement or publicly available data
• The modeled domain must be justified. Note that studies have shown that the vast majority of weathering in tailings piles occurs in the surface layer that is exposed to the atmosphere, provided that there is no mechanical overturn. By default, Project Proponents must model the top meter of the tailings pile
• The model, input data and output data used to calculate surficial feedstock weathering must be provided
• All assumptions and criteria for evaluating uncertainties in utilized models must be described. Assumptions about the storage conditions and potential reversal risks must be justified or substantiated with operational data. Where relevant, assumptions must be conservative

If the counterfactual fate of the feedstock is discharged into surface waters, some degree of carbon removal from ocean alkalinity enhancement (OAE) is expected. For projects where the feedstock would have counterfactual weathering via OAE:

• Project Proponents must provide a written description of the discharge process, discharge site and receiving ocean waters
• Weathering via OAE must be calculated using geochemical modeling of feedstock dissolution and subsequent air-sea gas exchange relevant to the receiving ocean waters. By default, it is assumed that all feedstock discharged into the ocean fully dissolves and remains in contact with the surface ocean, unless otherwise justified
• Models used to determine the proportion of feedstock dissolution must accurately reflect the feedstock mineralogy, surface area, and CDR potential, based on the data reported for feedstock characterization
• Models used to determine the proportion of feedstock dissolution must accurately reflect all the places where feedstock dissolution may occur (pre-processing of discharge, during discharge, during plume transport and dispersion, or upon settling). This may include interactions with other compounds prior to discharge, bulk freshwater, bulk seawater, or micro-environments which enhance feedstock dissolution, such as metabolic carbonate dissolution in submarine tailings piles
• Models used to determine the proportion of feedstock dissolution must accurately reflect the environmental conditions where dissolution may occur, including temperature, salinity, pH, carbonate saturation, organic matter deposition and remineralization, and sedimentation. Parameters may be directly measured or estimated conservatively
• The resulting atmospheric carbon removal from dissolved feedstock must follow the quantification approach outlined in Section 4.2.1.1 of the River and Ocean Losses Module
• The model, input data and output data used to calculate surficial feedstock weathering must be provided
• All assumptions must be described. Assumptions about the storage conditions must be justified or substantiated with operational data. Where relevant, assumptions must be conservative

Since this Module defines the durability of a Credit as 1,000+ years, the default timescale for modeling counterfactual feedstock weathering is 1000 years.

If additional information on the conditions and duration of feedstock storage at the feedstock supplier are available, Project Proponents may justify calculating the counterfactual across a time period relevant to the specific mine or quarry from which the feedstock is sourced in the PDD.

For example, projects operating in conjunction with active mines may find it appropriate to use the time of mine closure and provide details of the closure plan in the PDD. Alternatively, if sufficient documentation exists suggesting that piles of waste materials generated by the feedstock will not be exposed to ambient environmental conditions for a period exceeding a set number of years, the counterfactual may be considered across that time span.

Isometric would like to thank following reviewers of this Module:

• Michael T. Thorpe (University of Maryland and NASA Goddard Space Flight Center). Michael T. Thorpe's contribution to this Module was not part of his University of Maryland or NASA GSFC duties or responsibilities.
• Julianne DeAngelo (CREW Carbon)
• Will Savage (MEM Consultants)
• Jack Tucker (CarbonRun)
• Jonah Bernstein-Schalet (Mati Carbon)
• Amanda Stubbs (University of Glasgow)
• James Campbell, Ph.D. (Heriot-Watt University)
• Alison Marklein, Ph.D. (Terradot)
• Christina Larkin, Ph.D. (InPlanet)

This appendix outlines the various analytical techniques and measurements that may be used to satisfy the requirements and recommendations of this Module. The tables below summarize the analytical methods, the parameters they provide, their purpose in calculation of CO₂ removal and material characterization, and examples of acceptable standards. Required analyses will be pathway and project-specific, and Project Proponents must refer to specific Isometric Protocols for any additional pathway-specific requirements. This appendix is intended to provide a comprehensive, but not exhaustive, overview of analytical methods relevant to carbon dioxide removal calculations and feedstock characterization. All analytical methods used must be submitted for feedstock validation and, where applicable, cross-referenced with an appropriate standard (e.g. ISO, EN, BSI, ASTM and EPA) or standardized operating procedure. Where a project utilizes a non-standardized methodology or SOP for the determination of a listed parameter, the Project Proponent is required to outline the relevant method within the PDD submitted to the VVB.

Carbonate feedstocks

Please note that commercially produced carbonate feedstocks are exempt from having to comply with geotechnical and radioactivity measurements.

Note: The CoC template provided within this Appendix has been provided as an example for Project Proponents to build off. Rows should be expanded and added as required.

It is the responsibility of the Project Proponent to ensure all information is correct and compliant with any relevant national or international standards.

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8. Fedo, CM, and Babechuk, MG (2023). Petrogenesis of siliciclastic sediments and sedimentary rocks explored in three-dimensional Al2O3–CaO*+ Na2O–K2O–FeO+ MgO (A–CN–K–FM) compositional space. Canadian Journal of Earth Sciences, 60(7), 818-838. DOI: https://doi.org/10.1139/cjes-2022-0051 ↩

9. Thorpe, MT, Hurowitz, JA, Dehouck, E.(2019). Sediment geochemistry and mineralogy from a glacial terrain river system in southwest Iceland, Geochim. Cosmochim. Ac., 263, 140–166,DOI: https://doi.org/10.1016/j.gca.2019.08.003. ↩